This invention relates to a cooling medium circuit for an ice making machine and the like, which is designed to exhibit an improved defrosting and ice releasing capacity particularly under low temperature conditions when the frost deposited on the evaporator and the ice pieces formed in a freezing chamber are to be removed by feeding a high-temperature vaporized cooling medium to an evaporator.
An automatic ice making machine for making continuously a number of ice pieces such as cubes has a freezing circuit for circulating a cooling medium, in which the freezing chamber is designed to be heated by feeding a high-pressure and high-temperature vaporized cooling medium (hereinafter also referred to as hot gas) from the compressor to the evaporator attached to the freezing chamber, upon switching from freezing operation to ice releasing operation, to accelerate releasing of ice pieces formed in the ice chamber. FIG. 3, for example, shows a water injection system automatic ice making machine having a multiplicity of freezing cells opening downward to which the water to be frozen is injected to form ice cubes continuously. In this type of ice making machine, a freezing chamber 30 is disposed horizontally and has on the lower surface thereof partitions 32 intersecting one another to define a multiplicity of freezing cells 34 opening downward in a checkered pattern. An evaporator 18 communicating to a freezing circuit 22, shown in FIG. 4, runs zigzag in close contact with the upper surface of the freezing chamber 30 and forces to cool the freezing cells 34 by circulating a cooling medium during freezing operation. Meanwhile, a water tray 38 equipped with a water tank 36 in which the water to be frozen is contained is tiltably supported by a support shaft 40 immediately below the freezing chamber 30. The water tray 38 and the tank 36 are designed to be retained parallel to the freezing chamber 30 during freezing operation, whereas to be tilted clockwise on the support shaft 40 during ice releasing operation to open the freezing cells 34. A multiplicity of water jetting holes 42 and water recovering holes 44 are defined in the water tray 38 at the positions corresponding to the respective freezing cells; whereas a distribution pipe 48 communicating to a compression chamber 46 is provided on the lower surface of the water tray 38. The distribution pipe 48 also communicates to the water jetting holes 42. A pump 50 is provided on the outer surface of the tank 36 and designed to inject the water to be frozen into the respective freezing cells 34 through the distribution pipe 48 and the corresponding water jetting holes 42. The portion of the water which failed to freeze in the freezing cells 34 is recovered through the water recovering holes 44 into the tank 36.
FIG. 4 shows schematically a constitution of the freezing circuit to be suitably employed in the above-described automatic ice making machine. The freezing circuit 22 essentially has a compressor 10 for compressing a cooling medium such as Freon, a condenser 12 to which the high-pressure and high-temperature vaporized cooling medium compressed in the compressor 10 is fed, an expansion valve 16 to which the liquefied cooling medium through condensation in the condenser 12 is fed through a first solenoid valve V.sub.1 and an evaporator 18 to which the cooling medium expanded and vaporized through the expansion valve 16 is fed. Incidentally, a dryer 14 is interposed between the condenser 12 and the first solenoid valve V.sub.1, and the moisture in the cooling medium is designed to be removed thereby. The evaporator 18 performs heat exchange between the vaporized cooling medium expanded through the expansion valve 16 and the freezing chamber 30 attached to the evaporator 18 to cool the freezing chamber 30 below the freezing point and allow the water injected into the freezing cells 34 to be frozen gradually. The vaporized cooling medium heated after heat exchange in the evaporator 18 is fed back to the compressor 10, compressed to a high temperature and a high pressure and recirculated.
A pipe 28 branches out from the outlet side of the compressor 10 and is connected through a second solenoid valve V.sub.2 and a choking means 20 to the inlet side of the evaporator 18 to form a so-called hot gas circuit 24. The first solenoid valve V.sub.1 and the second solenoid valve V.sub.2 are designed to be switched over synchronously to assume states contrary to each other such that the first solenoid valve V.sub.1 may be open (ON) during freezing operation to allow the cooling medium to circulate through the freezing circuit 22. In this state, the second solenoid valve V.sub.2 is closed (OFF) to check circulation of the cooling medium through the hot gas circuit 24. Meanwhile, when ice releasing operation is started after completion of freezing operation in the freezing chamber 30 and ice cubes are allowed to fall, the state of the first solenoid valve V.sub.1 and that of the second solenoid valve V.sub.2 are changed over synchronously. Namely, the first solenoid valve V.sub.1 is closed (OFF) to check circulation of the cooling medium through the freezing circuit 22, while the second solenoid valve V.sub.2 is let open (ON) to allow the high-temperature cooling medium (hot gas) to circulate through the hot gas circuit 24. Thus, the freezing chamber 30 attached to the evaporator 18 is heated to release adhesion of the ice cubes formed in the respective freezing cells 34 and let them fall by their own weights.
As described above, when the ice making machine is switched to ice releasing operation, the state of the first solenoid valve V.sub.1 and that of the second solenoid valve V.sub.2 are changed over synchronously (1) to stop circulation of the cooling medium in the freezing circuit 22 and (2) to feed the high-pressure and high-temperature vaporized cooling medium from the outlet side of the compressor 10 to the evaporator 18. However, as shown in FIG. 4, while the outlet side of the condenser 12 is closed by the first solenoid valve V.sub.1 no closing means such as a valve is disposed to the inlet side of the condenser 12. Accordingly, the hot gas A delivered from the compressor 10 during ice releasing operation is not entirely fed to the hot gas circuit 24, but the substantial portion of the hot gas B is designed to be circulated through the hot gas circuit 24. A small amount of hot gas portion C flows into the condenser 12 where the heat of the hot gas is dissipated well and stays therein (this phenomenon is termed as "stagnation"). If some portion of the hot gas stagnates in the freezing circuit 22 connected to the condenser 12, the hot gas to be circulated through the hot gas circuit 24 decreases with time corresponding to the amount of stagnation C. It can thus be pointed out that the ice releasing capacity in the evaporator 18 is gradually lowered to require a considerable time for ice releasing operation, disadvantageously. Such problem occurs conspicuously when the ambient temperature is low. While problems occurring during freezing operation of the automatic ice making machine has been described, they are generally true with the freezing systems of freezers where defrosting is achieved by evaporators using a hot gas.